In manufacturing semiconductor devices, it is imperative that the devices are defect free at the time of production, and reliable throughout their use. When defects are found in completed devices, the percentage of usable devices increases, and the profitability of the manufacturer suffers. More importantly, when a semiconductor device fails after been installed a device, such a failure can cause the entire device to fail. That is, the failure of a single semiconductor device can render an entire consumer electronics device unusable. Accordingly, it is important that manufacturers of semiconductor devices minimize defects whenever possible.
One area where defects can occur as in the area of wire bonding. Wire bonds are used to connect a bond pad on one element of a device, such as a carrier wafer, to a bond pad on another element, such as a substrate receiving carrier wafer. Two types of wire bonding which are commonly used include ball bonding and wedge bonding. Gold-ball bonding is the most popular method. In this process, a melted sphere of gold bonds a length of wire down as a first bond. A loop drawn out from the first bond then connects the wire, and then reforms another ball for the subsequent ball bond. Gold-wire bonding is characterized as a thermosonic process, meaning that heat, ultrasonics, force, and time are all used to effect the bond. A second method of wire bonding is the wedge bonding process. This process is primarily used with aluminum wire but also can be used with gold wire. Usually performed at an ambient temperature, wedge bonding involves putting two wedge bonds down. No ball is formed in this process. This aluminum bond process is characterized as an ultrasonic wire bond, meaning only ultrasonic energy, force, and time are used to create the bond.
The use of these types of processes depends on the specific type of application. For example, gold-wire bonding is used in most high volume applications because it is a faster process. Aluminum-wire bonding is used in situations when packages or a PCB cannot be heated. In addition, the wedge bonding process can attain a finer pitch than gold-wire bonding. Gold-wire bonding, for example, requires smooth, clean bond surfaces. Typically, gold wire is bonded to an aluminum pad on the die and thick-or thin-film gold metallization on the substrate. The cleanliness of the substrate affects the reliability of the bond. Although organic contamination can be removed with a cleaning process, such as argon plasma cleaning, such removal requires additional time and expense.
When producing a carrier wafer having bond pads, a number of processing steps are performed before a wire bond is ever attached to the bond pad of the wafer carrier. In some instances, for example when a flip chip is attached to the carrier wafer, a bump pad on a carrier wafer for receiving a solder bump is formed at the same time that a wire bond pad is formed. While various steps for enabling a flip chip to be attached to the carrier wafer are performed on the bond pad, such as the application of an under bump metallization layer and the solder bump itself, the wire bond pad on the carrier wafer remains exposed. That is, the surface of the wire bond pad is often exposed to processing steps for other areas of the carrier wafer. Accordingly, the wire bond pad can often become contaminated, rendering the wire bond pad difficult to bond.
Accordingly, there is a need for an improved integrated circuit and method of producing an integrated circuit integrated circuit having improved wire bond pads.